JP7461147B2 - Sheet material and tray using same - Google Patents

Description

The present invention relates to a sheet material and a tray formed using this sheet material.

Conventionally, there are a large number of containers made of resin that are used to store food and daily necessities. The sheet material used to form such containers is required to have processability when forming the container, such as deep drawability and rollability, as well as rigidity and printability.

As an example, a multilayer sheet formed by laminating thermoplastic resin layers containing a filler has been proposed (Patent Document 1). According to this publication, a resin laminate sheet is proposed that includes a base layer made of rubber-modified polystyrene blended with 5 to 30% by weight of an inorganic filler, and a transparent surface layer having a printed surface made of polystyrene blended with 5 to 20% by weight of a styrene-butadiene block copolymer. This resin laminate sheet provides a resin laminate sheet with excellent deep drawability and incineration properties, as well as a smooth surface appearance. However, when this resin laminate sheet is molded into a container or the like, cracks and breaks are likely to occur depending on the molding method. In particular, because a film is laminated and only talc is actually used as the inorganic filler, cracks and breaks are likely to occur when the resin laminate sheet is manufactured or when a container or the like is molded from this resin laminate sheet. In addition, when calcium carbonate is used instead of talc, the rigidity is reduced.

Therefore, a multi-layer co-extruded sheet has been proposed in which outer layers made of resin such as polystyrene resin are laminated on both sides of an inner layer made of a resin composition in which a mixture of talc and calcium carbonate has been added to a resin component mainly made of polystyrene resin, and the thickness of each of the outer layers is 3% by weight or more of the total layer thickness (Patent Document 2). According to this publication, a multi-layer co-extruded sheet has been proposed in which outer layers (B) made of polystyrene resin and/or polyolefin resin are laminated on both sides of an inner layer (A) made of a resin composition in which talc and calcium carbonate have been added to a resin component made of polystyrene resin or a mixture of said polystyrene resin and polyolefin resin, and the thickness of each of the outer layers (B) is 3% by weight or more of the total layer thickness.

However, according to this publication, the combined ratio of talc and calcium carbonate is 15% by weight or more, and preferably 30 to 50% by weight, of the entire multilayer sheet, and a large amount of resin is blended in. If the resin content is high, a recycle mark is required, and there is a problem that waste disposal procedures differ depending on the local government.

Further, the above publication describes a polystyrene-based resin multilayer sheet and is based on the assumption that polystyrene-based resin is used, but when the present inventors conducted tests, it was found that when the tray was molded from polystyrene-based resin, the heat resistance was low. It also has low oil resistance and chemical resistance, and is expensive, making it unsuitable for food products containing oil or heating applications, such as food trays. In addition, since its impact resistance is inferior to that of other resin materials, there were concerns that the contents would be damaged or lose their shape when transported over long distances.

Japanese Patent Application Publication No. 4-341842 Patent No. 3542363

The present invention was made in light of this background. One of the objects of the present invention is to provide a sheet material that is easy to dispose of as general waste and has enhanced heat resistance, and a tray using the same.

Means for solving the problem and effects of the invention

In order to achieve the above object, a sheet material according to a first aspect of the present invention has a multilayer resin structure including an intermediate layer and a pair of surface layers formed on the front and back surfaces of the intermediate layer, respectively. The surface layer is a resin layer made of a polypropylene resin, the intermediate layer contains calcium carbonate, talc, and a polypropylene resin or a polyethylene resin , and the calcium carbonate and polyethylene resin in the entire sheet are The composition has a composition in which the combined ratio of talc is more than 50% by weight and not more than 75% by weight . With the above configuration, a sheet material with excellent workability and rigidity can be realized by combining calcium carbonate and talc. In addition , sheet materials with excellent heat resistance, cold resistance, and weather resistance can be realized.

Further, according to the sheet material according to the second aspect of the present invention, in addition to the above configuration, the intermediate layer does not contain polystyrene resin. With the above configuration, the heat resistance of the sheet material can be increased, making it suitable for applications that require heating, such as food trays. In particular, by not containing polystyrene, it can increase heat resistance, improve impact resistance, improve oil resistance and chemical resistance, and reduce costs.

Furthermore , according to the sheet material according to the third aspect of the present invention, in addition to any of the above configurations, the blending ratio of calcium carbonate and talc in the intermediate layer can be 1:1 to 1:10. With the above configuration, the problem of sheet rigidity, where calcium carbonate alone has relatively low rigidity, can be solved by increasing the ratio of talc.

Furthermore, according to a fourth aspect of the present invention, in addition to any one of the above configurations, the thickness of each surface layer can be set to 1% to 50% of the thickness of the intermediate layer.

Furthermore, according to the sheet material according to the fifth aspect of the present invention, in addition to any one of the above configurations, the thickness of the entire sheet can be set to 200 μm to 800 μm.

Furthermore, according to the sheet material according to the sixth aspect of the present invention, in addition to any of the above configurations, the thickness of the intermediate layer can be 100 μm to 780 μm.

Furthermore, according to the sheet material according to the seventh aspect of the present invention, in addition to any of the above structures, the surface layer can be formed of a homopolymer, a block copolymer, or a random copolymer.

Furthermore, according to the sheet material according to the eighth aspect of the present invention, in addition to any of the above configurations, the calcium carbonate is spherical and has an average particle size of 1 μm to 20 μm.

Furthermore, according to a sheet material according to a ninth aspect of the present invention, in addition to any one of the configurations described above, the entire sheet can contain 1% by weight to 25% by weight of calcium carbonate, 25% by weight to 50% by weight of talc, 20% by weight to 40% by weight of block copolymer, 10% by weight to 25% by weight of low-density polyethylene, or 10% by weight to 25% by weight of high-density polyethylene.

Furthermore, the sheet material according to the tenth aspect of the present invention can be used as a tray for food.

FIG. 2 is an enlarged cross-sectional view showing a sheet material according to an embodiment of the present invention.

Embodiments of the present invention will be described below based on the drawings. However, the examples shown below are illustrative of a sheet material and a container formed using this sheet material for embodying the technical idea of the present invention. The container to be molded is not limited to the following. Furthermore, this specification does not in any way limit the materials shown in the claims to the materials of the embodiments. In particular, the materials, shapes, relative positions thereof, etc. described in the embodiments are not intended to limit the scope of the present invention solely thereto, unless otherwise specified, and are merely illustrative examples. Note that the sizes, positional relationships, etc. of members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, each element constituting the present invention may be configured so that a plurality of elements are made of the same member so that one member serves as a plurality of elements, or conversely, the function of one member may be performed by a plurality of members. It can also be accomplished by sharing.
[Embodiment 1]
(Sheet material 30)

An enlarged cross-sectional view of the sheet material according to the first embodiment of the present invention is shown in FIG. 1. The sheet material 30 shown in this figure is a laminate in which a surface layer 31 is laminated on each surface of an intermediate layer 32. This sheet material is suitable for vacuum forming and can be suitably used for food trays and the like. Generally, JIS standards distinguish between sheets having a thickness of 250 μm or more and films having a thickness of less than 250 μm, but in this specification, the term "sheet material" also includes those having a thickness of less than 250 μm.

Vacuum forming involves applying heat to a sheet or plate of thermoplastic resin to soften it, pressing it into a convex or concave mold, and creating a near-vacuum state by sucking the air between the thermoplastic resin and the mold from below. , is a molding method in which a thermoplastic resin is brought into close contact with a mold to create the desired shape. It has the advantages of low mold production costs, the ability to make prototypes in a short period of time, low prototyping costs, large size, easy thin-wall molding, various shapes, easy partial design changes, and small-lot production. For example, it is used to manufacture parts trays, transport trays, resin covers, food trays, food packs, spoilers with simple shapes, motorcycle cowlings, etc.

Sheets of thermoplastic resins such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), and polystyrene (PS) are widely used for such vacuum-formed products. However, in recent years, molded products made by vacuum forming have been required to address environmental issues such as the depletion of petroleum resources and the disposal of waste. Therefore, in this embodiment, the ratio of resin in the entire sheet is suppressed to less than half. Here, the content ratio of inorganic substances is set to exceed 50% by weight. Specifically, the total blending ratio of calcium carbonate and talc in the entire sheet is set to exceed 50% by weight. By reducing the amount of petroleum-derived thermoplastic resin in this way, it contributes to the reduction of petroleum fuel and CO ₂ during combustion. In particular, by combining calcium carbonate and talc, it is possible to create sheet materials with excellent workability and rigidity. Furthermore, it is easier to dispose of it as general waste. According to the Containers and Packaging Recycling Law, containers and packaging are classified as main material containers based on weight among the materials that make up containers and packaging, so if containers are formed using sheet materials that contain more than 50% by weight of inorganic substances, Such containers are not classified as plastic containers and packaging, and can be easily disposed of as nonflammable materials by tearing or crushing them into a compact size. By mixing an inorganic substance into the vacuum forming sheet in this way, the amount of thermoplastic resin used can be reduced, and a container that can be easily disposed of and processed can be realized.
(Surface layer)

The intermediate layer contains calcium carbonate, talc, and resin. On the other hand, the surface layer 31 contains a polypropylene resin. In general, the inclusion of calcium carbonate reduces acid resistance. Therefore, by providing a surface layer made of polypropylene resin on both sides of the intermediate layer, the acid resistance of the sheet material 30 can be improved. In particular, when the sheet material is applied to food trays and the like by vacuum forming, it is possible to prevent calcium carbonate in the sheet material from being eluted by acid when it comes into contact with food.

Preferably, the surface layer is made of only polypropylene-based resin. By not including polyethylene-based resin in the surface layer 31, heat resistance can be improved. According to tests conducted by the present inventors, it was found that if the surface layer 31 contains a polyethylene-based resin such as LLDPE (linear low density polyethylene), the heat resistance decreases accordingly. Therefore, by excluding polyethylene-based resin from the surface layer, heat resistance is improved.

In particular, food containers for low-temperature storage are sometimes heated in ovens or microwaves after being sold with frozen or refrigerated foods stored in them. is also required. On the other hand, food containers for low-temperature storage such as frozen foods are also required to be cold resistant. Therefore, in order to increase heat resistance while maintaining cold resistance, polyethylene resin is not included in the surface layer, and the surface layer 31 is made only of polypropylene resin, thereby achieving both heat resistance and cold resistance. .

In addition, by selecting b-PP (block copolymer) from among polypropylene-based resins to form the surface layer 31, the specific gravity is reduced to reduce the weight and the rigidity is increased. The specific gravity of the entire sheet material is 1.50 or less, preferably 1.42. This weight reduction allows the sheet to be used as a food tray while maintaining its rigidity and being suitable for use. Alternatively, h-PP (homopolymer) or r-PP (random copolymer) may be used as the surface layer 31. h-PP has excellent rigidity and heat resistance, but is inferior in low-temperature impact resistance, which can be improved by copolymerizing a monomer such as ethylene. b-PP and r-PP have improved impact resistance. r-PP has improved heat sealability.
(Middle class)

The middle layer contains calcium carbonate, talc, and resin. The inclusion of calcium carbonate improves cold resistance, making it suitable for use in trays for frozen foods, etc.

Calcium carbonate is made into a spherical powder, and preferably has an average particle size of 1 μm to 20 μm. In this embodiment, the average particle diameter is 4 μm. The average particle size is the median diameter (D50) measured by laser diffraction method. Note that Microtrack (version 10.5.4-236B) manufactured by Nikkiso Co., Ltd. was used for the measurement. The use of calcium carbonate in the intermediate layer increases rigidity and provides resistance to drawdown during vacuum forming, resulting in a sheet material with excellent formability. Furthermore, as described above, acid resistance can be increased by covering the intermediate layer of the sheet material with a resin surface layer. With this configuration, the sheet material can be used without any problem even if food containing acid comes into direct contact with the sheet material, and can be suitably used as a food tray. On the other hand, using only calcium carbonate reduces the rigidity. Therefore, in the sheet material according to this embodiment, talc is further blended into the intermediate layer to improve rigidity and ensure moldability. This makes the punching process easier, and the shape of the punched tray can be stably maintained.

Further, the blending ratio of calcium carbonate and talc in the intermediate layer is preferably 1:1 to 1:10. By adjusting the blending ratio in this way, the problem that calcium carbonate alone has relatively low rigidity and is difficult to mold can be solved by increasing the talc ratio.

In addition, the intermediate layer resin does not contain polystyrene resin. As a result, the heat resistance of the sheet material can be increased, making it suitable for applications that require heating, such as food trays. Instead of polystyrene resin, polypropylene resin or polyethylene resin is used for the intermediate layer resin. Thereby, a sheet material with excellent heat resistance and weather resistance can be realized.

The thickness of each surface layer is preferably 1% to 50% of the thickness of the intermediate layer. If the intermediate layer is thicker, the PE ratio will be higher and cold resistance will be improved even if the structure is the same. Therefore, the intermediate layer is adjusted to be thicker than the surface layer. The overall thickness of the sheet material is preferably 200 μm to 800 μm. The intermediate layer is preferably 100 μm to 780 μm. The surface layer is preferably 10 μm or more and 50 μm or less. This makes it difficult for calcium carbonate to be exposed from the intermediate layer to the surface layer.
(Polyolefin modifier)

Furthermore, the intermediate layer may contain a polyolefin-based modifier. This provides effects such as improved impact resistance. The polyolefin-based modifier may be an ethylene-based copolymer or a propylene-based copolymer. For example, TAFMER A (ethylene-based copolymer), TAFMER BL (butene-based copolymer), TAFMER PN (propylene-based copolymer), etc., manufactured by Mitsui Chemicals, Inc., may be used.
(Coloring Agent)

Furthermore, a colorant may be included in the intermediate layer. For the colorant, a pellet material containing a white pigment is used. For example, a white master batch (MB) can be suitably used.

The ratio of b-PP in the intermediate layer 32 can be 20-40% by weight, preferably 20-30% by weight, and more preferably 20% by weight. By lowering the ratio of b-PP in the intermediate layer 32 relatively to that in the surface layer 31 in this way, the cold resistance can be improved, making it suitable as a tray for frozen foods.

Further, it is preferable to add LDPE (low density polyethylene) to the intermediate layer. This can be expected to improve cold resistance and further improve tensile elongation.

The overall composition of the sheet material is based on 1% by weight to 25% by weight of calcium carbonate, 25% by weight to 50% by weight of talc, 20% by weight to 40% by weight of b-PP, 10% by weight to 25% by weight of LDPE, or 10% by weight to 25% by weight of HDPE (high density polyethylene), and preferably contains 0.01% by weight to 10% by weight of a polyolefin modifier and 0.01% by weight to 5% by weight of a colorant. As an example, the composition of the intermediate layer is 25% by weight of calcium carbonate, 33% by weight of talc, 22% by weight of b-PP, and 20% by weight of LDPE, and the surface layer is b-PP. By configuring in this way, a sheet material with improved reproducibility of the shape when used in mold molding can be obtained. In particular, by reducing the resin content of the entire sheet material, it becomes easier to punch and has excellent processability. Furthermore, when formed into a food tray, for example, in a form in which food is divided into multiple compartments and individually packaged, if cut lines or perforations are provided to separate the compartments, it becomes easier for the user to tear the compartments by hand, which is advantageous in terms of usability.
(Tensile elongation)

Further, the tensile elongation rate of the sheet material is preferably 20% to 600%. This is advantageous for vacuum forming. Note that the tensile elongation rate disclosed in this specification was measured according to JIS.

By using calcium carbonate in the middle layer, the tensile elongation is improved, and the tensile force of the sheet is increased when the sheet material is melted during vacuum forming, making it suitable for forming. In addition, by using talc in the middle layer, the rigidity is increased, and the sheet material has the strength required for tray loading after punching, which is an advantage of making it into a sheet material with excellent formability.
[Example 1, Comparative Examples 1 to 4]

Next, sheet materials were prepared as Examples 1 to 6 and Comparative Examples 1 to 5, and the thickness, density, tensile stress, and elongation rate of each were measured. The results are shown in Table 1. Regarding the tensile stress and elongation rate, the values at 23° C. were measured in the transport direction (MD direction) during sheet production and in the direction perpendicular to the transport direction (TD direction). Further, the tensile elongation rate was in accordance with JIS standard K7161-1:2014 (ISO527-1:2012).

In Comparative Example 1, ultra-cold-resistant PP (PP + PE) manufactured by L Package Co., Ltd. was used, and in Comparative Example 2, MAPKA (paper 51% by weight) manufactured by the Environmental Management Research Institute was used. Comparative Examples 3 to 5 and Examples 1 to 6 are sheet materials manufactured by Shinwa Plastic Co., Ltd. with different resin blend ratios. Comparative Example 3 is 26% by weight talc, 26% by weight LLDPE, 23% by weight b-PP, 13% by weight h-PP, 9% by weight HDPE, and 3% by weight colored MB. Comparative Example 4 is 50% by weight talc, 31% by weight b-PP, 17% by weight LDPE, and 2% by weight colored MB. Comparative Example 5 is 50% by weight calcium carbonate, 31% by weight b-PP, 17% by weight LDPE, and 2% by weight colored MB. Example 1 is 29% by weight talc, 22% by weight calcium carbonate, 31% by weight b-PP, and 18% by weight LDPE. In Example 2, 38% by weight of talc, 13% by weight of calcium carbonate, 31% by weight of b-PP, and 18% by weight of LDPE were used; in Example 3, 47% by weight of talc, 4% by weight of calcium carbonate, 31% by weight of b-PP, and 18% by weight of LDPE; in Example 4, 29% by weight of talc, 22% by weight of calcium carbonate, 31% by weight of b-PP, and 18% by weight of HDPE; in Example 5, 38% by weight of talc, 13% by weight of calcium carbonate, 31% by weight of b-PP, and 18% by weight of HDPE; and in Example 6, 47% by weight of talc, 4% by weight of calcium carbonate, 31% by weight of b-PP, and 18% by weight of HDPE were used.

As a result, it was confirmed that the elongation rate tends to decrease as more talc is added, and that the selection of LDPE rather than HDPE as the resin to be used in combination can suppress the decrease in elongation rate in both MD and TD. The decrease in tensile stress is also suppressed to a range that is acceptable for manufacturing such as forming, and a practical value is ensured compared to the paper of Comparative Example 2. Furthermore, the thickness can be made thinner compared to the paper of Comparative Example 2 and the talc of Comparative Example 3. As a result, it was confirmed that the elongation rate tends to decrease as more talc is added, and that the selection of LDPE rather than HDPE as the resin to be used in combination can suppress the decrease in elongation rate in both MD and TD. In this way, a lower tensile stress allows the sheet to be fitted to a mold with a weaker force, which is advantageous for formability. In this way, it was confirmed that the sheet material of the embodiment has excellent formability.

The sheet material of the present invention is suitable for use as a sheet material for forming containers for storing food and other daily necessities.

30... Sheet material 31... Surface layer 32... Intermediate layer

Claims (10)

middle class and
A resin sheet material with a multilayer structure comprising a pair of surface layers formed on the front and back surfaces of the intermediate layer,
The surface layer is a resin layer made of polypropylene resin,
The intermediate layer contains calcium carbonate, talc, polypropylene resin or polyethylene resin,
A sheet material having a composition in which the combined blending ratio of calcium carbonate and talc in the entire sheet is more than 50% by weight and less than 75% by weight . 2. The sheet material according to claim 1,
The sheet material, wherein the intermediate layer does not contain a polystyrene-based resin. The sheet material according to claim 1 or 2 ,
A sheet material in which the blending ratio of calcium carbonate and talc in the intermediate layer is 1:1 to 1:10. The sheet material according to any one of claims 1 to 3 ,
A sheet material in which the thickness of each surface layer is 1% to 50% of the thickness of the intermediate layer. The sheet material according to any one of claims 1 to 4 ,
A sheet material whose total sheet thickness is 200 μm to 800 μm. The sheet material according to any one of claims 1 to 5 ,
A sheet material in which the intermediate layer has a thickness of 100 μm to 780 μm. The sheet material according to any one of claims 1 to 6 ,
The sheet material, wherein the surface layer is any one of a homopolymer, a block copolymer, and a random copolymer. The sheet material according to any one of claims 1 to 7 ,
A sheet material in which the calcium carbonate is spherical and has an average particle size of 1 μm to 20 μm. The sheet material according to any one of claims 1 to 8 ,
The sheet material is composed of 1% to 25% by weight of calcium carbonate, 25% to 50% by weight of talc, 20% to 40% by weight of block copolymer, 10% to 25% by weight of low density polyethylene, or 10% to 25% by weight of high density polyethylene, based on the entire sheet. The sheet material according to any one of claims 1 to 9 ,
A sheet material used as a food tray.

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